Electronic modules used in automotive applications often employ electronic components mounted to a printed circuit board. The electronic components are typically soldered to the printed circuit boards and electrically coupled to metal traces overlying the surface of the printed circuit board. Typically, for automotive control applications, several large power transistors are mounted to the printed circuit board. To reduce product cost, it is desirable to utilize standard packaged devices, such as the TO-220 device, in electronic modules intended for automotive control applications. For example, in automotive applications, such as an ignition control system, the TO-220 power transistors are typically used as ignition coil drivers. The TO-220 devices are capable of generating large quantities of heat during normal operation. To keep the temperature of the power transistors from rising to a destructive level, heat-dissipating structures are generally employed to conduct the heat away from the transistors.
In heat dissipation techniques of the prior art, the printed circuit board is adhesively bonded to a metal, baseplate. The baseplate generally has high thermal conductivity and is the primary thermoradiator to the ambient environment. To effectively transfer the heat from electronic components mounted on the printed circuit board to the baseplate, the total thermal resistance between the electronic components and the baseplate must be minimized. The adhesive bonding layer is typically an organic polymer that provides the primary attachment of the printed circuit board to the baseplate. However, the adhesive bonding layer accounts for the majority of the thermal resistance between the electronic components and the baseplate. This problem is compounded by the use of plastic packaging encasing the electronic components. The plastic packaging adds an additional layer of thermal resistance between the baseplate and the electronic component.
Often, electronic modules are required to function in a high temperature ambient environment. In this embodiment, large amounts of power must be dissipated from the electronic devices within the electronic module. The commonly used thick ceramic substrates are soldered to the baseplate during fabrication of the electronic module. In addition to high cost, these substrates do not offer exceptional thermal performance, nor do they permit multilayer substrate configurations to be fabricated. Also, the module fabrication process requires numerous processing steps.
Accordingly, further development of module fabrication technology is necessary to improve the temperature control, and to provide a low-cost improved configuration of electronic modules containing heat-generating electronic components.